Prostate Cancer
Prostate cancer is the most prevalent cancer in men and is the second leading cause of death from cancer among males in the United States. AJCC Cancer Staging Handbook 203 (Irvin D. Fleming et al. eds., 5th ed. 1998); Walter J. Burdette, Cancer: Etiology, Diagnosis, and Treatment 147 (1998). The American Cancer Society estimated there will be 234,460 new cases of prostate cancer and 27,350 deaths in 2005. Additionally, the rate of prostate cancer deaths in the United States for 1997-2001 was 31.5 per 100,000 men, second only to lung and bronchus cancer. American Cancer Society website: cancer with the extension .org of the world wide web. Cancer of the prostate typically occurs in older males, with a median age of 74 years for clinical diagnosis. Burdette, supra at 147. A man's risk of being diagnosed with invasive prostate cancer in his lifetime is one in six. Platz et al., supra at 21.
Although our understanding of the etiology of prostate cancer is incomplete, the results of extensive research in this area point to a combination of age, genetic and environmental/dietary factors. Platz et al., supra at 19; Burdette, supra at 147; Steven K. Clinton, Diet and Nutrition in Prostate Cancer Prevention and Therapy, in Prostate Cancer: a Multidisciplinary Guide 246-269 (Philip W. Kantoff et al. eds. 1997). Broadly speaking, genetic risk factors predisposing one to prostate cancer include race and a family history of the disease. Platz et al., supra at 19, 28-29, 32-34. Aside from these generalities, a deeper understanding of the genetic basis of prostate cancer has remained elusive. Considerable research has been directed to studying the link between prostate cancer, androgens, and androgen regulation, as androgens play a crucial role in prostate growth and differentiation. Meena Augustus et al., Molecular Genetics and Markers of Progression, in Management of Prostate Cancer 59 (Eric A Klein ed. 2000). While a number of studies have concluded that prostate tumor development is linked to elevated levels of circulating androgen (e.g., testosterone and dihydrotestosterone), the genetic determinants of these levels remain unknown. Platz et al., supra at 29-30.
Several studies have explored a possible link between prostate cancer and the androgen receptor (AR) gene, the gene product of which mediates the molecular and cellular effects of testosterone and dihydrotestosterone in tissues responsive to androgens. Id. at 30. Differences in the number of certain trinucleotide repeats in exon 1, the region involved in transactivational control, have been of particular interest. Augustus et al., supra at 60. For example, these studies have revealed that as the number of CAG repeats decreases the transactivation ability of the gene product increases, as does the risk of prostate cancer. Platz et al., supra at 30-31. Other research has focused on the α-reductase Type 2 gene, the gene which codes for the enzyme that converts testosterone into dihydrotestosterone. Id. at 30. Dihydrotestosterone has greater affinity for the AR than testosterone, resulting in increased transactivation of genes responsive to androgens. Id. While studies have reported differences among the races in the length of a TA dinucleotide repeat in the 3′ untranslated region, no link has been established between the length of that repeat and prostate cancer. Id. Interestingly, while ras gene mutations are implicated in numerous other cancers, such mutations appear not to play a significant role in prostate cancer, at least among Caucasian males. Augustus, supra at 52.
Environmental/dietary risk factors which may increase the risk of prostate cancer include intake of saturated fat and calcium. Platz et al., supra at 19, 25-26. Conversely, intake of selenium, vitamin E and tomato products (which contain the carotenoid lycopene) apparently decrease that risk. Id. at 19, 26-28 The impact of physical activity, cigarette smoking, and alcohol consumption on prostate cancer is unclear. Platz et al., supra at 23-25.
Periodic screening for prostate cancer is most effectively performed by digital rectal examination (DRE) of the prostate, in conjunction with determination of the serum level of prostate-specific antigen (PSA). Burdette, supra at 148. While the merits of such screening are the subject of considerable debate, Jerome P. Richie & Irving D. Kaplan, Screening for Prostate Cancer: The Horns of a Dilemma, in Prostate Cancer: A Multidisciplinary Guide 1-10 (Philip W. Kantoff et al. eds. 1997), the American Cancer Society and American Urological Association recommend that both of these tests be performed annually on men 50 years or older with a life expectancy of at least 10 years, and younger men at high risk for prostate cancer. Ian M. Thompson & John Foley, Screening for Prostate Cancer, in Management of Prostate Cancer 71 (Eric A Klein ed. 2000). If necessary, these screening methods may be followed by additional tests, including biopsy, ultrasonic imaging, computerized tomography, and magnetic resonance imaging. Christopher A. Haas & Martin I. Resnick, Trends in Diagnosis, Biopsy, and Imaging, in Management of Prostate Cancer 89-98 (Eric A Klein ed. 2000); Burdette, supra at 148.
Once the diagnosis of prostate cancer has been made, treatment decisions for the individual are typically linked to the stage of prostate cancer present in that individual, as well as his age and overall health. Burdette, supra at 151. One preferred classification system for staging prostate cancer was developed by the American Urological Association (AUA). Id. at 148. The AUA classification system divides prostate tumors into four broad stages, A to D, which are in turn accompanied by a number of smaller substages. Burdette, supra at 152-153; Anthony V. D'Amico et al., The Staging of Prostate Cancer, in Prostate Cancer: A Multidisciplinary Guide 41 (Philip W. Kantoff et al. eds. 1997).
Stage A prostate cancer refers to the presence of microscopic cancer within the prostate gland. D'Amico, supra at 41. This stage is comprised of two substages: A1, which involves less than four well-differentiated cancer foci within the prostate, and A2, which involves greater than three well-differentiated cancer foci or alternatively, moderately to poorly differentiated foci within the prostate. Burdette, supra at 152; D'Amico, supra at 41. Treatment for stage A1 preferentially involves following PSA levels and periodic DRE. Burdette, supra at 151. Should PSA levels rise, preferred treatments include radical prostatectomy in patients 70 years of age and younger, external beam radiotherapy for patients between 70 and 80 years of age, and hormone therapy for those over 80 years of age. Id.
Stage B prostate cancer is characterized by the presence of a palpable lump within the prostate. Burdette, supra at 152-53; D'Amico, supra at 41. This stage is comprised of three substages: B1, in which the lump is less than 2 cm and is contained in one lobe of the prostate; B2, in which the lump is greater than 2 cm yet is still contained within one lobe; and B3, in which the lump has spread to both lobes. Burdette, supra, at 152-53. For stages B1 and B2, the treatment again involves radical prostatectomy in patients 70 years of age and younger, external beam radiotherapy for patients between 70 and 80 years of age, and hormone therapy for those over 80 years of age. Id. at 151. In stage B3, radical prostatectomy is employed if the cancer is well-differentiated and PSA levels are below 15 ng/mL; otherwise, external beam radiation is the chosen treatment option. Id.
Stage C prostate cancer involves a substantial cancer mass accompanied by extraprostatic extension. Burdette, supra at 153; D'Amico, supra at 41. Like stage A prostate cancer, Stage C is comprised of two substages: substage C1, in which the tumor is relatively minimal, with minor prostatic extension, and substage C2, in which the tumor is large and bulky, with major prostatic extension. Id. The treatment of choice for both substages is external beam radiation. Burdette, supra at 151.
The fourth and final stage of prostate cancer, Stage D, describes the extent to which the cancer has metastasized. Burdette, supra at 153; D'Amico, supra at 41. This stage is comprised of four substages: (1) D0, in which acid phosphatase levels are persistently high, (2) D1, in which only the pelvic lymph nodes have been invaded, (3) D2, in which the lymph nodes above the aortic bifurcation have been invaded, with or without distant metastasis, and (4) D3, in which the metastasis progresses despite intense hormonal therapy. Id. Treatment at this stage may involve hormonal therapy, chemotherapy, and removal of one or both testes. Burdette, supra at 151.
Despite the need for accurate staging of prostate cancer, current staging methodology is limited. The wide variety of biological behavior displayed by neoplasms of the prostate has resulted in considerable difficulty in predicting and assessing the course of prostate cancer. Augustus et al., supra at 47. Indeed, despite the fact that most prostate cancer patients have carcinomas that are of intermediate grade and stage, prognosis for these types of carcinomas is highly variable. Andrew A Renshaw & Christopher L. Corless, Prognostic Features in the Pathology of Prostate Cancer, in Prostate Cancer: A Multidisciplinary Guide 26 (Philip W. Kantoff et al. eds. 1997). Techniques such as transrectal ultrasound, abdominal and pelvic computerized tomography, and MRI have not been particularly useful in predicting local tumor extension. D'Amico, supra at 53 (editors' comment). While the use of serum PSA in combination with the Gleason score is currently the most effective method of staging prostate cancer, id., PSA is of limited predictive value, Augustus et al., supra at 47; Renshaw et al., supra at 26, and the Gleason score is prone to variability and error, King, C. R. & Long, J. P., Int'l. J. Cancer 90(6): 326-30 (2000). As such, the current focus of prostate cancer research has been to obtain biomarkers to help better assess the progression of the disease. Augustus et al., supra at 47; Renshaw et al., supra at 26; Pettaway, C. A., Tech. Urol. 4(1): 35-42 (1998).
Accordingly, there is a great need for more sensitive and accurate methods for predicting whether a person is likely to develop prostate cancer, for diagnosing prostate cancer, for monitoring the progression of the disease, for staging the prostate cancer, for determining whether the prostate cancer has metastasized and for imaging the prostate cancer. There is also a need for better treatment of prostate cancer.
Colon Cancer
Colorectal cancer is the second most common cause of cancer death in the United States and the third most prevalent cancer in both men and women. M. L. Davila & A. D. Davila, Screening for Colon and Rectal Cancer, in Colon and Rectal Cancer 47 (Peter S. Edelstein ed., 2000). Colorectal cancer is categorized as a digestive system cancer by the American Cancer Society (ACS) which also includes cancers of the esophagus, stomach, small intestine, anus, anal canal, anorectum, liver & intrahepatic bile duct, gallbladder & other biliary, pancreas, and other digestive organs. The ACS estimates that there will be about 263,060 new cases of digestive system cancers in 2006 in the United States alone. Digestive system cancers will cause an estimated 136,180 deaths combined in the United States in 2006. Specifically, The ACS estimates that there will be about 104,950 new cases of colon cancer, 40,340 new cases of rectal cancer and 5,420 new cases of small intestine cancer in the 2005 in the United States alone. Colon, rectal and small intestine cancers will cause an estimated 57,360 deaths combined in the United States in 2005. ACS Website: cancer with the extension .org of the world wide web. Nearly all cases of colorectal cancer arise from adenomatous polyps, some of which mature into large polyps, undergo abnormal growth and development, and ultimately progress into cancer. Davila at 55-56. This progression would appear to take at least 10 years in most patients, rendering it a readily treatable form of cancer if diagnosed early, when the cancer is localized. Davila at 56; Walter J. Burdette, Cancer: Etiology, Diagnosis, and Treatment 125 (1998).
Although our understanding of the etiology of colon cancer is undergoing continual refinement, extensive research in this area points to a combination of factors, including age, hereditary and nonhereditary conditions, and environmental/dietary factors. Age is a key risk factor in the development of colorectal cancer, Davila at 48, with men and women over 40 years of age become increasingly susceptible to that cancer, Burdette at 126. Incidence rates increase considerably in each subsequent decade of life. Davila at 48. A number of hereditary and nonhereditary conditions have also been linked to a heightened risk of developing colorectal cancer, including familial adenomatous polyposis (FAP), hereditary nonpolyposis colorectal cancer (Lynch syndrome or HNPCC), a personal and/or family history of colorectal cancer or adenomatous polyps, inflammatory bowel disease, diabetes mellitus, and obesity. Id. at 47; Henry T. Lynch & Jane F. Lynch, Hereditary Nonpolyposis Colorectal Cancer (Lynch Syndromes), in Colon and Rectal Cancer 67-68 (Peter S. Edelstein ed., 2000).
Environmental/dietary factors associated with an increased risk of colorectal cancer include a high fat diet, intake of high dietary red meat, and sedentary lifestyle. Davila at 47; Reddy, B. S., Prev. Med. 16(4): 460-7 (1987). Conversely, environmental/dietary factors associated with a reduced risk of colorectal cancer include a diet high in fiber, folic acid, calcium, and hormone-replacement therapy in post-menopausal women. Davila at 50-55. The effect of antioxidants in reducing the risk of colon cancer is unclear. Davila at 53.
Because colon cancer is highly treatable when detected at an early, localized stage, screening should be a part of routine care for all adults starting at age 50, especially those with first-degree relatives with colorectal cancer. One major advantage of colorectal cancer screening over its counterparts in other types of cancer is its ability to not only detect precancerous lesions, but to remove them as well. Davila at 56. The key colorectal cancer screening tests in use today are fecal occult blood test, sigmoidoscopy, colonoscopy, double-contrast barium enema, and the carcinoembryonic antigen (CEA) test. Burdette at 125; Davila at 56.
The fecal occult blood test (FOBT) screens for colorectal cancer by detecting the amount of blood in the stool, the premise being that neoplastic tissue, particularly malignant tissue, bleeds more than typical mucosa, with the amount of bleeding increasing with polyp size and cancer stage. Davila at 56-57. While effective at detecting early stage tumors, FOBT is unable to detect adenomatous polyps (premalignant lesions), and, depending on the contents of the fecal sample, is subject to rendering false positives. Davila at 56-59. Sigmoidoscopy and colonoscopy, by contrast, allow direct visualization of the bowel, and enable one to detect, biopsy, and remove adenomatous polyps. Davila at 59-60, 61. Despite the advantages of these procedures, there are accompanying downsides: sigmoidoscopy, by definition, is limited to the sigmoid colon and below, colonoscopy is a relatively expensive procedure, and both share the risk of possible bowel perforation and hemorrhaging. Davila at 59-60. Double-contrast barium enema (DCBE) enables detection of lesions better than FOBT, and almost as well a colonoscopy, but it may be limited in evaluating the winding rectosigmoid region. Davila at 60. The CEA blood test, which involves screening the blood for carcinoembryonic antigen, shares the downside of FOBT, in that it is of limited utility in detecting colorectal cancer at an early stage. Burdette at 125.
Once colon cancer has been diagnosed, treatment decisions are typically made in reference to the stage of cancer progression. A number of techniques are employed to stage the cancer (some of which are also used to screen for colon cancer), including pathologic examination of resected colon, sigmoidoscopy, colonoscopy, and various imaging techniques. AJCC Cancer Staging Handbook 84 (Irvin D. Fleming et al. eds., 5th ed. 1998); Montgomery, R. C. and Ridge, J. A., Semin. Surg. Oncol. 15(3): 143-150 (1998). Moreover, chest films, liver functionality tests, and liver scans are employed to determine the extent of metastasis. Fleming at 84. While computerized tomography and magnetic resonance imaging are useful in staging colorectal cancer in its later stages, both have unacceptably low staging accuracy for identifying early stages of the disease, due to the difficulty that both methods have in (1) revealing the depth of bowel wall tumor infiltration and (2) diagnosing malignant adenopathy. Thoeni, R. F., Radiol. Clin. N. Am. 35(2): 457-85 (1997). Rather, techniques such as transrectal ultrasound (TRUS) are preferred in this context, although this technique is inaccurate with respect to detecting small lymph nodes that may contain metastases. David Blumberg & Frank G. Opelka, Neoadjuvant and Adjuvant Therapy for Adenocarcinoma of the Rectum, in Colon and Rectal Cancer 316 (Peter S. Edelstein ed., 2000). Several classification systems have been devised to stage the extent of colorectal cancer, including the Dukes' system and the more detailed International Union against Cancer-American Joint Committee on Cancer TNM staging system, which is considered by many in the field to be a more useful staging system. Burdette at 126-27. The TNM system, which is used for either clinical or pathological staging, is divided into four stages, each of which evaluates the extent of cancer growth with respect to primary tumor (T), regional lymph nodes (N), and distant metastasis (M). Fleming at 84-85. The system focuses on the extent of tumor invasion into the intestinal wall, invasion of adjacent structures, the number of regional lymph nodes that have been affected, and whether distant metastasis has occurred. Fleming at 81.
Stage 0 is characterized by in situ carcinoma (Tis), in which the cancer cells are located inside the glandular basement membrane (intraepithelial) or lamina propria (intramucosal). In this stage, the cancer has not spread to the regional lymph nodes (N0), and there is no distant metastasis (M0). In stage I, there is still no spread of the cancer to the regional lymph nodes and no distant metastasis, but the tumor has invaded the submucosa (T1) or has progressed further to invade the muscularis propria (T2). Stage II also involves no spread of the cancer to the regional lymph nodes and no distant metastasis, but the tumor has invaded the subserosa, or the nonperitonealized pericolic or perirectal tissues (T3), or has progressed to invade other organs or structures, and/or has perforated the visceral peritoneum (T4). Stage III is characterized by any of the T substages, no distant metastasis, and either metastasis in 1 to 3 regional lymph nodes (N1) or metastasis in four or more regional lymph nodes (N2). Lastly, stage IV involves any of the T or N substages, as well as distant metastasis. Fleming at 84-85; Burdette at 127.
Currently, pathological staging of colon cancer is preferable over clinical staging as pathological staging provides a more accurate prognosis. Pathological staging typically involves examination of the resected colon section, along with surgical examination of the abdominal cavity. Fleming at 84. Clinical staging would be a preferred method of staging were it at least as accurate as pathological staging, as it does not depend on the invasive procedures of its counterpart.
Turning to the treatment of colorectal cancer, surgical resection results in a cure for roughly 50% of patients. Irradiation is used both preoperatively and postoperatively in treating colorectal cancer. Chemotherapeutic agents, particularly 5-fluorouracil, are also powerful weapons in treating colorectal cancer. Other agents include irinotecan and floxuridine, cisplatin, levamisole, methotrexate, interferon-α, and leucovorin. Burdette at 125, 132-33. Nonetheless, thirty to forty percent of patients will develop a recurrence of colon cancer following surgical resection, which in many patients is the ultimate cause of death. Wayne De Vos, Follow-up After Treatment of Colon Cancer, Colon and Rectal Cancer 225 (Peter S. Edelstein ed., 2000). Accordingly, colon cancer patients must be closely monitored to determine response to therapy and to detect persistent or recurrent disease and metastasis.
The next few paragraphs describe the some of molecular bases of colon cancer. In the case of FAP, the tumor suppressor gene APC (adenomatous polyposis coli), chromosomally located at 5q21, has been either inactivated or deleted by mutation. Alberts et al., Molecular Biology of the Cell 1288 (3d ed. 1994). The APC protein plays a role in a number of functions, including cell adhesion, apoptosis, and repression of the c-myc oncogene. N. R. Hall & R. D. Madoff, Genetics and the Polyp-Cancer Sequence, Colon and Rectal Cancer 8 (Peter S. Edelstein, ed., 2000). Of those patients with colorectal cancer who have normal APC genes, over 65% have such mutations in the cancer cells but not in other tissues. Alberts et al., supra at 1288. In the case of HPNCC, patients manifest abnormalities in the tumor suppressor gene HNPCC, but only about 15% of tumors contain the mutated gene. Id. A host of other genes have also been implicated in colorectal cancer, including the K-ras, N-ras, H-ras and c-myc oncogenes, and the tumor suppressor genes DCC (deleted in colon carcinoma) and p53. Hall & Madoff, supra at 8-9; Alberts et al., supra at 1288.
Abnormalities in Wg/Wnt signal transduction pathway are also associated with the development of colorectal carcinoma. Taipale, J. and Beachy, P. A. Nature 411: 349-354 (2001). Wnt1 is a secreted protein gene originally identified within mouse mammary cancers by its insertion into the mouse mammary tumor virus (MMTV) gene. The protein is homologous to the wingless (Wg) gene product of Drosophila, in which it functions as an important factor for the determination of dorsal-ventral segmentation and regulates the formation of fly imaginal discs. Wg/Wnt pathway controls cell proliferation, death and differentiation. Taipal (2001). There are at least 13 members in the Wnt family. These proteins have been found expressed mainly in the central nervous system (CNS) of vertebrates as well as other tissues such as mammary and intestine. The Wnt proteins are the ligands for a family of seven transmembrane domain receptors related to the Frizzled gene product in Drosophila. Binding Wnt to Frizzled stimulates the activity of the downstream target, Disheveled, which in turn inactivates the glycogen synthetase kinase 3β (GSK3β). Taipal (2001). Usually active GSK3β will form a complex with the adenomatous polyposis coli (APC) protein and phosphorylate another complex member, β-catenin. Once phosphorylated, β-catenin is directed to degradation through the ubiquitin pathway. When GSK3β or APC activity is down regulated, β-catenin is accumulated in the cytoplasm and binds to the T-cell factor or lymphocyte excitation factor (Tcf/Lef) family of transcriptional factors. Binding of β-catenin to Tcf releases the transcriptional repression and induces gene transcription. Among the genes regulated by β-catenin are a transcriptional repressor Engrailed, a transforming growth factor-β (TGF-β) family member Decapentaplegic, and the cytokine Hedgehog in Drosophila. β-Catenin also involves in regulating cell adhesion by binding to α-catenin and E-cadherin. On the other hand, binding of β-catenin to these proteins controls the cytoplasmic β-catenin level and its complexing with TCF. Taipal (2001). Growth factor stimulation and activation of c-src or v-src also regulate β-catenin level by phosphorylation of α-catenin and its related protein, p120cas. When phosphorylated, these proteins decrease their binding to E-cadherin and β-catenin resulting in the accumulation of cytoplasmic β-catenin. Reynolds, A. B. et al. Mol. Cell Biol. 14: 8333-8342 (1994). In colon cancer, c-src enzymatic activity has been shown increased to the level of v-src. Alternation of components in the Wg/Wnt pathway promotes colorectal carcinoma development. The best known modifications are to the APC gene. Nicola S et al. Hum. Mol. Genet 10:721-733 (2001). This germline mutation causes the appearance of hundreds to thousands of adenomatous polyps in the large bowel. It is the gene defect that accounts for the autosomally dominantly inherited FAP and related syndromes. The molecular alternations that occur in this pathway largely involve deletions of alleles of tumor-suppressor genes, such as APC, p53 and Deleted in Colorectal Cancer (DCC), combined with mutational activation of proto-oncogenes, especially c-Ki-ras. Aoki, T. et al. Human Mutat. 3: 342-346 (1994). All of these lead to genomic instability in colorectal cancers.
Another source of genomic instability in colorectal cancer is the defect of DNA mismatch repair (MMR) genes. Human homologues of the bacterial mutHLS complex (hMSH2, hMLHI, hPMS1, hPMS2 and hMSH6), which is involved in the DNA mismatch repair in bacteria, have been shown to cause the HNPCC (about 70-90% HNPCC) when mutated. Modrich, P. and Lahue, R. Ann Rev. Biochem. 65: 101-133 (1996); and Peltomaki, P. Hum. Mol. Genet 10: 735-740 (2001). The inactivation of these proteins leads to the accumulation of mutations and causes genetic instability that represents errors in the accurate replication of the repetitive mono-, di-, tri- and tetra-nucleotide repeats, which are scattered throughout the genome (microsatellite regions). Jass, J. R. et al. J. Gastroenterol Hepatol 17: 17-26 (2002). Like in the classic FAP, mutational activation of c-Ki-ras is also required for the promotion of MSI in the alternative HNPCC. Mutations in other proteins such as the tumor suppressor protein phosphatase PTEN (Zhou, X. P. et al. Hum. Mol. Genet 11: 445-450 (2002)), BAX (Buttler, L. M. Aus. N. Z. J. Surg. 69: 88-94 (1999)), Caspase-5 (Planck, M. Cancer Genet Cytogenet. 134: 46-54 (2002)), TGFβ-RII (Fallik, D. et al. Gastroenterol Clin Biol. 24: 917-22 (2000)) and IGFII-R (Giovannucci E. J. Nutr. 131: 3109S-20S (2001)) have also been found in some colorectal tumors possibly as the cause of MMR defect.
Some tyrosine kinases have been shown up-regulated in colorectal tumor tissues or cell lines like HT29. Skoudy, A. et al. Biochem J. 317 (Pt 1): 279-84 (1996). Focal adhesion kinase (FAK) and its up-stream kinase c-src and c-yes in colonic epithelia cells may play an important role in the promotion of colorectal cancers through the extracellular matrix (ECM) and integrin-mediated signaling pathways. Jessup, J. M. et al., The molecular biology of colorectal carcinoma, in: The Molecular Basis of Human Cancer, 251-268 (Coleman W. B. and Tsongalis G. J. Eds. 2002). The formation of c-src/FAK complexes may coordinately deregulate VEGF expression and apoptosis inhibition. Recent evidences suggest that a specific signal-transduction pathway for cell survival that implicates integrin engagement leads to FAK activation and thus activates PI-3 kinase and akt. In turn, akt phosphorylates BAD and blocks apoptosis in epithelial cells. The activation of c-src in colon cancer may induce VEGF expression through the hypoxia pathway. Other genes that may be implicated in colorectal cancer include Cox enzymes (Ota, S. et al. Aliment Pharmacol. Ther. 16 (Suppl 2): 102-106 (2002)), estrogen (al-Azzawi, F. and Wahab, M. Climacteric 5: 3-14 (2002)), peroxisome proliferator-activated receptor-γ (PPAR-γ) (Gelman, L. et al. Cell Mol. Life Sci. 55: 932-943 (1999)), IGF-I (Giovannucci (2001)), thymine DNA glycosylase (TDG) (Hardeland, U. et al. Prog. Nucleic Acid Res. Mol. Biol. 68: 235-253 (2001)) and EGF (Mendelsohn, J. Endocrine-Related Cancer 8: 3-9 (2001)).
Gene deletion and mutation are not the only causes for development of colorectal cancers. Epigenetic silencing by DNA methylation also accounts for the lost of function of colorectal cancer suppressor genes. A strong association between MSI and CpG island methylation has been well characterized in sporadic colorectal cancers with high MSI but not in those of hereditary origin. In one experiment, DNA methylation of MLH1, CDKN2A, MGMT, THBS1, RARB, APC, and p14ARF genes has been shown in 80%, 55%, 23%, 23%, 58%, 35%, and 50% of 40 sporadic colorectal cancers with high MSI respectively. Yamamoto, H. et al. Genes Chromosomes Cancer 33: 322-325 (2002); and Kim, K. M. et al. Oncogene. 12; 21(35): 5441-9 (2002). Carcinogen metabolism enzymes such as GST, NAT, CYP and MTHFR are also associated with an increased or decreased colorectal cancer risk. Pistorius, S. et al. Kongressbd Dtsch Ges Chir Kongr 118: 820-824 (2001); and Potter, J. D. J. Natl. Cancer Inst. 91: 916-932 (1999).
From the foregoing, it is clear that procedures used for detecting, diagnosing, monitoring, staging, prognosticating, and preventing the recurrence of colorectal cancer are of critical importance to the outcome of the patient. Moreover, current procedures, while helpful in each of these analyses, are limited by their specificity, sensitivity, invasiveness, and/or their cost. As such, highly specific and sensitive procedures that would operate by way of detecting novel markers in cells, tissues, or bodily fluids, with minimal invasiveness and at a reasonable cost, would be highly desirable.
Accordingly, there is a great need for more sensitive and accurate methods for predicting whether a person is likely to develop colorectal cancer, for diagnosing colorectal cancer, for monitoring the progression of the disease, for staging the colorectal cancer, for determining whether the colorectal cancer has metastasized, and for imaging the colorectal cancer. Following accurate diagnosis, there is also a need for less invasive and more effective treatment of colorectal cancer.
In addition to prostate and digestive tract cancers, there is great need for improved methods and compounds for the detection, diagnosis, prognosis, imaging, determination of metastases and metastatic potential, monitoring, staging and treatment of lung, liver, pancreatic, bone and esophagus cancers.
Angiogenesis in Cancer
Growth and metastasis of solid tumors are also dependent on angiogenesis. Folkman, J., 1986, Cancer Research, 46, 467-473; Folkman, J., 1989, Journal of the National Cancer Institute, 82, 4-6. It has been shown, for example, that tumors which enlarge to greater than 2 mm must obtain their own blood supply and do so by inducing the growth of new capillary blood vessels. Once these new blood vessels become embedded in the tumor, they provide a means for tumor cells to enter the circulation and metastasize to distant sites such as liver, lung or bone. Weidner, N., et al., 1991, The New England Journal of Medicine, 324(1), 1-8.
Angiogenesis, defined as the growth or sprouting of new blood vessels from existing vessels, is a complex process that primarily occurs during embryonic development. The process is distinct from vasculogenesis, in that the new endothelial cells lining the vessel arise from proliferation of existing cells, rather than differentiating from stem cells. The process is invasive and dependent upon proteolysis of the extracellular matrix (ECM), migration of new endothelial cells, and synthesis of new matrix components. Angiogenesis occurs during embryogenic development of the circulatory system; however, in adult humans, angiogenesis only occurs as a response to a pathological condition (except during the reproductive cycle in women).
Under normal physiological conditions in adults, angiogenesis takes place only in very restricted situations such as hair growth and wounding healing. Auerbach, W. and Auerbach, R., 1994, Pharmacol Ther. 63(3):265-3 11; Ribatti et al., 1991, Haematologica 76(4):3 11-20; Risau, 1997, Nature 386(6626):67 1-4. Angiogenesis progresses by a stimulus which results in the formation of a migrating column of endothelial cells. Proteolytic activity is focused at the advancing tip of this “vascular sprout”, which breaks down the ECM sufficiently to permit the column of cells to infiltrate and migrate. Behind the advancing front, the endothelial cells differentiate and begin to adhere to each other, thus forming a new basement membrane. The cells then cease proliferation and finally define a lumen for the new arteriole or capillary.
Unregulated angiogenesis has gradually been recognized to be responsible for a wide range of disorders, including, but not limited to, cancer, cardiovascular disease, rheumatoid arthritis, psoriasis and diabetic retinopathy. Folkman, 1995, Nat Med 1(1):27-31; Isner, 1999, Circulation 99(13): 1653-5; Koch, 1998, Arthritis Rheum 41(6):951-62; Walsh, 1999, Rheumatology (Oxford) 38(2):103-12; Ware and Simons, 1997, Nat Med 3(2): 158-64.
Of particular interest is the observation that angiogenesis is required by solid tumors for their growth and metastases. Folkman, 1986 supra; Folkman 1990, J Natl. Cancer Inst., 82(1) 4-6; Folkman, 1992, Semin Cancer Biol 3(2):65-71; Zetter, 1998, Annu Rev Med 49:407-24. A tumor usually begins as a single aberrant cell which can proliferate only to a size of a few cubic millimeters due to the distance from available capillary beds, and it can stay ‘dormant’ without further growth and dissemination for a long period of time. Some tumor cells then switch to the angiogenic phenotype to activate endothelial cells, which proliferate and mature into new capillary blood vessels. These newly formed blood vessels not only allow for continued growth of the primary tumor, but also for the dissemination and recolonization of metastatic tumor cells. The precise mechanisms that control the angiogenic switch is not well understood, but it is believed that neovascularization of tumor mass results from the net balance of a multitude of angiogenesis stimulators and inhibitors Folkman, 1995, supra.
One of the most potent angiogenesis inhibitors is endostatin identified by O'Reilly and Folkman. O'Reilly et al., 1997, Cell 88(2):277-85; O'Reilly et al., 1994, Cell 79(2):3 15-28. Its discovery was based on the phenomenon that certain primary tumors can inhibit the growth of distant metastases. O'Reilly and Folkman hypothesized that a primary tumor initiates angiogenesis by generating angiogenic stimulators in excess of inhibitors. However, angiogenic inhibitors, by virtue of their longer half life in the circulation, reach the site of a secondary tumor in excess of the stimulators. The net result is the growth of primary tumor and inhibition of secondary tumor. Endostatin is one of a growing list of such angiogenesis inhibitors produced by primary tumors. It is a proteolytic fragment of a larger protein: endostatin is a 20 kDa fragment of collagen XVIII (amino acid H1132-K1315 in murine collagen XVIII). Endostatin has been shown to specifically inhibit endothelial cell proliferation in vitro and block angiogenesis in vivo. More importantly, administration of endostatin to tumor-bearing mice leads to significant tumor regression, and no toxicity or drug resistance has been observed even after multiple treatment cycles. Boehm et al., 1997, Nature 390(6658):404-407. The fact that endostatin targets genetically stable endothelial cells and inhibits a variety of solid tumors makes it a very attractive candidate for anticancer therapy. Fidler and Ellis, 1994, Cell 79(2):185-8; Gastl et al., 1997, Oncology 54(3):177-84; Hinsbergh et al., 1999, Ann Oncol 10 Suppl 4:60-3. In addition, angiogenesis inhibitors have been shown to be more effective when combined with radiation and chemotherapeutic agents. Klement, 2000, J. Clin Invest, 105(8) R15-24. Browder, 2000, Cancer Res. 6-(7) 1878-86, Arap et al., 1998, Science 279(5349):377-80; Mauceri et al., 1998, Nature 394(6690):287-91.
As discussed above, each of the methods for diagnosing and staging prostate, colon, lung or pancreas cancer is limited by the technology employed. Accordingly, there is need for sensitive molecular and cellular markers for the detection of prostate, colon, lung or pancreas cancer. There is a need for molecular markers for the accurate staging, including clinical and pathological staging, of prostate, colon, lung or pancreas cancers to optimize treatment methods. In addition, there is a need for sensitive molecular and cellular markers to monitor the progress of cancer treatments, including markers that can detect recurrence of prostate, colon, lung or pancreas cancers following remission.
The present invention provides alternative methods of treating prostate, colon, lung or pancreas cancer that overcome the limitations of conventional therapeutic methods as well as offer additional advantages that will be apparent from the detailed description below.